The present invention relates generally to a Silicon On Insulator (SOI) device and a method for fabricating the same, and more particularly, to a SOI device that can obtain a floating body effect as well as prevent punch-through and a method for fabricating the same.
In the semiconductor industry it is considered desirable to have a device with high integration, high speed, and low power consumption. One approach to realizing high integration, high speed, and a lower power consumption is a semiconductor device that utilizes a Silicon On Insulator (SOI) substrate rather than a substrate made of bulk silicon (hereinafter, a semiconductor device utilizing a SOI substrate is referred to as an “SOI device”). The advantages of an SOI device over a device formed with a substrate made of bulk silicon include: high speed due to low junction capacitance, low power consumption due to a low threshold voltage, and removal of latch-up due to complete isolation.
The SOI device is formed on a SOI substrate made of the following: a silicon substrate that supports the entire device, a silicon layer on which a gate is formed, and a filled oxide layer formed between the silicon substrate and the silicon layer. The gate is formed on the SOI substrate and a junction region is formed at both sides of the gate within the silicon layer.
This SOI device increases the effective channel length of the transistor, and thus can improve a short channel effect and can also minimize Drain Induced Barrier Lowering (DIBL) or a phenomenon in which interference between a source region and a drain region occurs. In addition, the SOI device can obtain a floating body effect since the body portion is isolated by the junction region and the buried oxide layer; and therefore, the floating body can store charges. Accordingly, a separate capacitor for storing charges is not needed, and the cell size can be reduced to 6F2 and 4F2.
However, in a conventional SOI device, although the junction region is formed at both sides of the gate within the surface of the silicon layer, the lower end of the junction region does not adjoin the buried oxide layer. Therefore, since the channel region i.e. the body of the transistor cannot be isolated by the junction region and the buried oxide layer, the floating body effect cannot be obtained.
It is possible to solve the aforementioned problem by carrying out an ion implantation process for forming the junction region at a dose that is high enough to make the lower end portion of the junction region fully adjoin the portion of the buried oxide layer therebelow. However, in this case, the distance between adjacent junction regions is decreased since when the junction region is formed it extends not only in a vertical direction but also in a horizontal direction within the silicon layer. As a consequence, punch-through may occur as the effective channel length of the transistor is reduced.